Illuminant
A light defined by a spectral distribution energy which may or may not be physically realized as a source

Illuminant A
Light that is represented by a tunsten filament lamp (yellow/orange in color) operated at a temperature of 2854 °K

Illuminant C
Light representative of overcast daylight having a color temperature of 6700 °K

Illuminant D65
Light representative of overcast daylight having a color temperature of 6500 °K. This illuminant is a more accurate representation of natural daylight than illuminant C.

Illuminant F (Cool White Fluorescent; CWF)
A fluorescent light represented by the GE Cool White lamp having a color temperature of 4200 °K

Illuminant TL84
A fluorescent light which represents a specific 3-band fluorescent lamp having a color temperature of 4000 °K

Illuminant Ultralume 3000 (U30)
Energy efficient fluorescent source (prime color lamp) having a color temperature of 3000 °K.

Internal Reflectance (Int %R)
That portion of the incident light flux which is trapped within the sample due to reflection of the light at the inside surface of the sample.

K
Kubleka Munk coefficient of absorption

K/S
A ratio of the Kubleka Munk constants, K (coefficient of absorption), and S (coefficient of scattering)

Kubleka Munk Theory
A theory that describes the optical behavior of materials which scatter and absorb radiant energy.

l
CMC relative tolerance for lightness.

L*, L
Abbreviation for lightness which is generally used in color order systems to describe the perceived amount of light reflected or transmitted by materials.

Lightness
The impression of the relative amount of incident light that a surface reflects. It varies from a minimum (for black) to a maximum (for white).